Fig. 4. Sharp wave ripple complexes in vitro (mouse hippocampal CA1 minislice) do not require GABA_A receptors.

When GABA_A receptors are blocked, the complexes can be evoked by pressure ejection of KCl (1 M) into stratum radiatum (upper traces), although they do not occur spontaneously. A: stratum radiatum field potential of KCl-evoked sharp wave ripple, in 10 µM gabazine to block GABA_A receptors. 150–300 Hz filtered trace shown below, highlighting the ripple. B: combined extracellular (above) and intracellular (putative pyramidal cell, below) recordings, during KCl-induced sharp wave ripple, with GABA_A receptors blocked. The cell was held at −70mV (left), to show the compound glutamatergic EPSP during the sharp wave, without phasic IPSPs. [Phasic IPSPs do occur in baseline conditions, in vivo (Ylinen et al., 1995) and in vitro (Maier et al., 2003).] When the cell was held depolarized at −47 mV (right), it generated a burst during the sharp wave ripple, but again without evidence of phasic IPSPs. From Nimmrich et al. (2005).